# Physics Paper 3 Questions and Answers with Confidential - Momaliche Post Mock 2020 Exam

• Answer ALL questions in the spaces provided in the question paper.
• You are supposed to spend the first 15 minutes of the 2 ½ hrs allowed for this paper reading the whole paper carefully before commencing your work.
• Marks are given for a clear record of the observations actually made, their suitability, accuracy and the use made of them.
• Candidates are advised to record their observations as soon as they are made.
• Non-programmable silent electronic calculators and KNEC mathematical tables may be used except where stated otherwise.

Question one

You are provided with the following:

• 2 new dry cells size D
• A cell holder
• A switch
• A milliammeter of range 0 to 1 mA
• A capacitor labeled C (2200μF)
• 8 connecting wires; at least four with crocodile clips on one end
• A stopwatch
• A carbon resistor labeled R (4.7KΩ)

Proceed as follows

1. Connect the circuit as shown in the figure 1below, where P and Q are crocodile clips.
2. Close the switch S
3. Name the process which takes place when the switch S is closed    (1 mark)
4. Connect the crocodile clips P and Q. Observe and record the highest reading of the milliammeter Io ( This is the current at t0 = 0)
Io = ………………………………………………………………. mA (1 mark)
5. While the milliammeter show the maximum value of current Io, open the switch S and start the stop watch simultaneously. Stop the stop watch when the current has dropped from Io to 0.5 mA. Read and record in the table below the time taken
6. Reset the stop watch and close the switch. Repeat the procedure in (e) to measure and record the time taken for the current to drop from Io to each of the other values shown in the table below. (5 marks)
 Current I (mA 0.5 0.4 0.3 0.2 0.1 Time t (s)
7. Plot a graph of Current I (y – axis)(mA) against time t (s) (5 marks)
8. From your graph, find W the value of I when t = 10s. (3 marks)
9. Given that A = 10W, determine the value of A. (3 marks)
10. Determine the voltage across R at t = 10s given that R = 4.7kΩ (2 marks)

Question Two

You are provided with the following;

• a rectangular glass block
• 4 optical pins
• 2 thumb pins
• a soft board
• a plain paper

Proceed as follows:

1. Place the glass block on the plain paper with one of the largest face upper most. Trace round the glass block using a pencil as shown below.
2. Remove the glass block and construct a normal at B. Construct an incident ray AB of angle of incidence, i = 20°.
3. Measure the breadth b of the glass bloc
4. Replace the glass block and trace the ray ABCD using the optical pins.
5. Remove the glass block and draw the path of the ray ABCD using a pencil.
6. Measure the length L and record it in the table below
 Angle i0 L (cm) L2(cm)2 1/L2 (cm −2) Sin2i 20 0.1170 30 0.25 40 0.4312 50 0.5868 60 0.75 70 0.8830
7. Repeat the procedure above for the angles of incidence given.
8. Calculate the values of 1/L2 and record in the table above.
9. Plot a graph of 1/L2 (y-axis) against Sin2i. (5 marks)
10. Calculate the gradient S of the graph (3 marks)
11. Given that the equation of that graph is; 1/L2 = − (1/n2b2 ) Sin2i + 1/b2
Determine the value of n (3 marks)
12. Present your work sheet; attached to the exam paper (2 mark)

## MARKING SCHEME

Question one

1.
2.
3. Charging
4. Io  = 0.61   mA  ±0.02
5.
6.
 Current I (mA 0.5 0.4 0.3 0.2 0.1 Time t (s) 0.2 0.26 3.7 6.5 8.6
7.
8. W = 0.23
(confirm the value from the graph)
9. A= 10 × 0.23 × 10−3
10. V = IR
= 2.3 X 10-4 x 4.7 X 103

Question two

1.
2.
3. breadth b = 6.0 ± 0.2
4.
5.
6.
 Angle i0 L (cm) L2(cm)2 1/L2 (cm −2) Sin2i 20 6.2 38.44 0.026 0.1170 30 6.4 40.96 0.0244 0.25 40 6.7 44.89 0.0223 0.4312 50 7.1 50.41 0.0198 0.5868 60 7.4 54.76 0.0183 0.75 70 7.6 57.76 0.0173 0.8830
7.
8.
9.
10.
Slope =  ∆½ = (24 − 10) × 10−3 =0.14
∆sin2   (14 − 3) × 10−1      1.1
=0.0127272cm−2
11. Gradient = 0.0127272 =  1/n2b2
1
/n2  = 0.4581812
n=1.47734
12. Confirm that the student presents a correct worked out diagram

CONFIDENTIAL

Question one

You are provided with the following:

• 2 new dry cells size D
• A cell holder
• A switch
• A milliammeter of range 0 to 1 mA
• A capacitor labeled C (2200μF)
• 8 connecting wires; at least four with crocodile clips on one end
• A stopwatch
• A carbon resistor labeled R (4.7KΩ)

Question two

You are provided with the following;

• a rectangular glass block; 9.6cm × 6.0cm × 2.4cm (Tolerance + or −0.2cm
• 4 optical pins
• 2 thumb pins
• a soft board
• a plain paper

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